We propose to continue our efforts at determining the chemical pathways involved in the oxidation of cholesterol and related unsaturated lipids by oxidizing agents which may occur in polluted air with particular attention being given to electronically excited (singlet) molecular oxygen. We shall be examining several model systems in which singlet molecular oxygen may be generated, including those involving peroxide anion. We shall also utilize cholesterol as a key model compound to attempt to determine whether hydroxyl radical formed by reaction between superoxide and peroxide anions will attack lipids as well. These studies will provide a complete picture of the nature of the oxidation pathways and products thereof, as they may be encountered in tissues and cellular membranes, which information in turn may suggest possible means of counteraction of any deleterious effects associated therewith. BIBLIOGRAPHIC REFERENCES: " Sterol Metabolism. XXXIV. On the Derivation of Carcinogenic Sterols from Cholesterol", L.L. Smith and M.J. Kulig, Cancer Biochem. Biophys., 1, 79-84 (1975). "Oxidations of Cholesterol in Model Systems Simulating Biological Conditions", L.L. Smith, M.J. Kulig, and J.I. Teng, Abstracts of Papers, 1st Chem. Congress of the North American Continent, Mexico City, November 30 - December 5, 1975, p. BMPC-75.